In the aluminum industry, large rolling ingots are produced by conducting molten metal from a furnace to a casting station, in which two or more ingots are formed by spraying coolant directly against the sides of each ingot while feeding molten metal to the top. The level of the top of the ingot remains substantially constant as the ingot is slowly lowered. A trough extends across the tops of each in-line group of ingots being cast, and from each trough a plurality of spouts (e.g., two to six or more for large rolling ingots) extend down to supply molten metal from each spout to the top of an ingot. Flow through each spout is controlled by a pin to plug the opening from the trough into the spout. Each pin extends up through the molten metal in the trough and is operated by a stem connected to the top of the pin. Each stem is connected to means for raising or lowering the stem and the pin attached to it. A gate upstream of all the spout openings controls flow into the trough from the furnace. A single platen supports all of the starting blocks of the ingots supplied by the trough, so that all of the ingots drop at the same time and rate.
When starting up a casting operation, all of the pins beneath the trough are raised enough to provide full flow, or a predetermined partially restricted flow, into the spouts, and then the upstream gate is fully opened. As soon as an of the ingots has received enough metal to start the drop, the platen starts down and the drop begins for all of the ingots beneath the trough.
This system of starting a direct chill casting drop has long been in general use when casting through mold rings which are in contact with the perimeter of each ingot. However, when electromagnetic force (EMF) is substituted for mold contact, the start-up conditions are more critical and the proportion of ingots which crack during start-up increases undesirably. The presence of the control pins causes turbulence in the stream of molten metal flowing through the trough during start-up. The amount of such turbulence varies among the different openings from the trough into the spouts, and the net result is that flow to the spouts is not evenly distributed during start-up, when using the conventional system described above.